Selective dimensional control of fine wire mesh

ABSTRACT

A method of selectively increasing or building up the thickness of a fine wire or wire mesh by means of an electron beam evaporation and deposition process. The resultant fine wire has a generally elongated rectangular cross-section. The crosssectional dimension of the resultant fine wire or mesh along the major axis substantially exceeds the dimension along the minor axis.

United States Patent [191 Balthis et a1.

[4 1 Oct. 14, 1975 SELECTIVE DIMENSIONAL CONTROL OF FINE WIRE MESH [75]Inventors: David L. Balthis, Ellicott City;

Frank A. Lindberg, Baltimore, both of Md.

[73] Assignee: Westinghouse Electric Corporation,

Pittsburgh, Pa.

22 Filed: Jan. 25, 1974 21 Appl. No.: 436,589

[52] US. Cl. 29/l 9l.6; 29/198; 427/42; 427/118; 427/120; 427/124;427/247 [51] Int. Cl. B21C 37/04; B23? 3/10 [58] Field of Search117/227, 231, 107, 128, 117/106 R, 93.3; 29/1935, 191.6, 198

[56] References Cited UNITED STATES PATENTS 3,655,428 4/1972 Bragardl17/93.3 X

3,779,802 12/1973 Streel 117/107X Primary Examiner-Mayer WeinblattAttorney, Agent, or FirmW. G. Sutcliff ABSTRACT A method of selectivelyincreasing or building up the thickness of a fine wire or wire mesh bymeans of an electron beam evaporation and deposition process. Theresultant fine wire has a generally elongated rectangular cross-section.The cross-sectional dimension of the resultant fine wire or mesh alongthe major axis substantially exceeds the dimension along the minor axis.

11 Claims, 3 Drawing Figures US. Patent 00. 14, 1975 POWER SUPPLY 26BACKGROUND OF THE INVENTION DESCRIPTION OF THE PREFERRED EMBODIMENT Thepresent invention can be best understood by ref- The present inventionrelates to the manufacture of 5 rence t0 the exemplary embodiments shownin the fine conductive wire and of providing such wire with an elongatedgenerally rectangular cross-section. Fine conductive wire, and moreparticularly meshes constructed of such fine wire, are used as grids inelectronic vidicon camera tubes, electron storage tubes, and other suchelectron devices. By fine mesh is meant a mesh wherein the wiredimension is between about 0.1 mil. to several mils in diameter. Suchfine mesh is typically formed from a thin plate-like member which has aplurality of symmetrical apertures through the member. Such aperturescan be provided by forming the member by an electroplating process, orby a etching process. The transmission area of the mesh, that is thepercentage of open area, can vary from for example about 20 to 90%transmission, with the number of wires varying for example from about 50to 2,000 wires per inch. Such mesh is very fragile and requires verycareful handling in order to avoid tearing or stretching. Such mesh isalso subjected to significant electrical stress due to the highelectrical fields in an operating device which can tend to deform themesh. A present method of increasing the mechanical strength of suchfine wire meshes is to increase the cross-sectional area of the wires ofthe mesh. Such meshes are usually formed by an etching orelectro-forming or plating process. All such prior art techniquesincrease the wire cross-section uniformly so that the resultant wireremains substantially uniform in cross-section with the width equal tothe thickness, and this results in a reduction in mesh transmission.This reduction in mesh transmission is undesirable and limits usage ofthe wire, or limits the increase in cross-sectional area for a givenapplication.

SUMMARY OF THE PRESENT INVENTION A method of producing fine wire or wiremesh in which the wire has an elongated, generally rectangularcross-section is detailed. An initially uniform crosssection wire isunidirectionally built up by an electron beam evaporation process tosignificantly strengthen the wire or mesh without reducing thetransmission of the formed mesh. The electron beam evaporation chamberis maintained at below about 8 X 10' Torr to insure that a substantiallyunidirectional build-up occurs.

In this way fine wire or mesh of selected conductive material can beprovided which has an elongated generally oval cross-section. The wiretypically has an approximate dimension of from 0.1 to 1 mil, in a firstdirection, and a dimension in a second direction normal to the firstdirection which exceeds the first direction dimension by greater thanabout a 2 to 1 ratio.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematical representationof a system for practicing the present invention.

FIG. 2 is an enlarged side elevational view of a fine wire mesh of thepresent invention.

FIG. 3 is a sectional view taken along lines IIIIII of FIG. 2.

drawings. In FIG. 1, an electron beam evaporation chamber 10 isschematically represented. The electron beam evaporation chamber 10 isconnected by an inlet manifold 12 via valve 14 to a high vacuum system16 which permits evacuation of the chamber 10 and maintenance of thechamber 10 at a relatively low pressure of below about 8 X 10" Torr andpreferably about 10* Torr.

A four pocket water cooled copper crucible 18 is disposed within thechamber 10 and is incorporated with the electron beam source 22. Theelectron beam source 22 is connected by high voltage input line 24 to anexternally disposed high voltage power supply 26. The electron beam isfocused and deflected through a 270 deflection angle by magneticfocusing and deflection coils, which are not shown. Such electron beamevaporation systems are well known and are commercially available fromAirco Temescal Company of Berkeley, California. The electron beam isfocused onto the surface of the conductive metal 28 which is disposedwithin the proper pocket of the multiple crucible 18. The evaporablemetal 28 is typically nickel which is supplied as evaporation grade or99.999% purity nickel shot, which has an average diameter of from aboutone-eighth to one-quarter inch. The metal pieces melt and flow togetherto form one large slug in the crucible when heated by the electron beam.A thin shell or skull of metal in contact with the water cooled crucibleremains frozen or solid.

The generally planar fine mesh 30, seen in FIG. 2 in greater detail, isdisposed within chamber 10 above the crucible 18 and spaced therefrom bya distance of about 6 to 8 inches. The planar mesh is disposed in aplane perpendicular to a line normal to the crucible. The fine mesh issupported above the crucible by means 32. An infrared heater means 34 isprovided within the chamber 10 disposed above the mesh 30 and spacedtherefrom, by for example about 4 inches. The heater 34 is connected toan appropriate power supply disposed outside of the chamber 10.

The fine mesh 30 is by way of example a generally planar member which isabout 0.16 mils thick and has a plurality of apertures therethrough, sothat the structural grids are spaced at about 500 grids per inch.

In practicing the present invention the chamber 10 is evacuated to a lowpressure of about 10 Torr and the valve 14 is open during theevaporation process. The infrared heaters are operated at a power inputof about 1,500 watts for about 45 minutes prior to the evaporation toheat the mesh 30 to promote adherence of the later deposited materialthereon. The electron beam is thereafter initiated, typically at about 5to 10 kilowatts electron beam power, to heat and evaporate the nickeldisposed within the crucible 18. The evaporated nickel will be depositedupon the mesh disposed above the crucible 18 and more particularly uponthe mesh surface facing the crucible. The evaporated metalwill beunidirectionally deposited upon the exposed surface of the planar mesh,and a significant build up in this direction will occur. The metaldeposited in this manner builds up thickness in the direction of thesource of the material without a corresponding increase in width of thedeposited material or of the mesh. In this way, the thickness of themesh can be selectively increased without significantly reducing themesh transmission. The resultant dimension along the direction of buildup for the wire described above is to provide a wire which is about 1.6mils thick. This provides a significant increase in the dimension of thewire in the direction of deposition. There is a slight increase in thewidth of the wire in the direction normal to the thickness build up, butthis is typically of the order of about a increase in the width. Thisrelatively small increase in the width of the wire of the mesh thusminimizes the reduction in transmission of the mesh. The thickness ofthe resultant wire exceeds the width by about a 10 to 1 ratio.

The wire described above as nickel can be other conductive metals suchas copper, aluminum, gold, titanium, and similar conductive elements andalloys. The evaporable metal may be the same metal as the wire substrateor can be another compatible metal. Thus the evaporable metal may by wayof example be gold, nickel, tantalum, or silver.

It is sometimes desirable in depositing a selected metal upon the wiresubstrate to first deposit a thin layer of an adherence promoting metal.For a nickel wire substrate, it is desirable to first electron beamevaporate and deposit a tantalum layer of about 1000 Angstromsthickness, again upon the surface of the wire or mesh exposed to orfacing the crucible. A plurality of crucibles are provided within thechamber in practicing this embodiment. The crucibles are movable intothe position indicated in FIG. 1 where the electron beam is focused ontothe metal surface within the crucible. The evaporated tantalum willdeposit on the nickel substrate and actually tend to embed itself in thenickel wire surface. The nickel containing crucible is then moved to thebeam focus point to permit evaporation and deposition of nickel onto thefreshly deposited tantalum. The rate of deposition of the metal upon thewire mesh is a function of the electron beam power input and for examplefor nickel with an electron beam power input of SKW approximately 1.5mils. is deposited in about 10 minutes. The thickness of metal depositedis observed by means ofa crystal monitor. The sensor of which isdisposed within the chamber so that as the metal is deposited upon thecrystal surface the resonant frequency of the crystal changes as afunction of the metal thickness. The thickness of the film is shown on adigital display.

It should be apparent that the wire or mesh substrate may be aninsulator as well as being a conductive substrate. 1n the same way, thedeposited material may be other than a conductive metal. The basis forproducing the unidirectional build-up will work with any material thatis evaporable at the low chamber pressure of less than about 8 X 10Torr.

The structural members provided by the present invention have improvedmechanical rigidity which broadens their application in electronicdevices.

We claim:

1. Method of producing fine wire having an elongated generallyrectangular cross-section, which wire has a cross-section which in afirst direction is of a predetermined dimension, and in a seconddirection normal to the first direction has a significantly greaterdimension, which method comprises:

a. disposing a wire within an evacuated chamber which is maintained atless than about 8 X 10 Torr pressure, with the wire disposed above anevaporable source of material disposed within said chamber;

b. heating said wire to promote adherence of the later depositedmaterial;

c. directing an electron beam onto said source of material to evaporatesaid material and deposit said material upon the heated wire surfaceexposed to the source of material so that the dimension in the directionnormal to the surface exposed to said material source is increased.

2. The method specified in claim 1, wherein said wire comprises agenerally planar fine wire mesh.

3. The method specified in claim 1, wherein the wire is preferablynickel of from 0.1 to 1 mil thick, and a first tantalum layer iselectron beam evaporated and deposited thereon, after which nickel iselectron beam evaporated and deposited on the tantalum.

4. The method specified in claim 3, wherein the fine wire is initiallyapproximately from 0.1 to 1 mil in thickness and the deposition increaseis substantially only in the wire thickness.

5. The method specified in claim 1 wherein successive layers ofdifferent material are sequentially evaporated by electron beam heatingand deposited upon the heated wire surface.

6. The method specified in claim 5, wherein for a nickel wire startingmaterial, tantalum is first evaporated and deposited upon the nickelwire, and thereafter nickel is evaporated and deposited atop thetantalum.

7. The method specified in claim 1 wherein the electron beam power is upto about 10,000 watts.

,8. The method specified in claim 1, wherein the wire is heated at apower input of about 500-1500 watts for about 45 minutes prior to theelectron beam evaporation deposition process.

9. The method specified in claim 1 wherein the wire comprises a finemesh, with the wire thickness being between 0.1 to 1 mil, and the meshhas up to about 2000 wires per inch.

10. Fine wire of selected conductive material having an elongatedgenerally rectangular cross-section produced by the method of:

a. disposing a uniform cross-section wire mesh within an evacuatedchamber which is maintained at less than about 8 X 10 Torr pressure,with the wire mesh being disposed above an evaporable source of materialdisposed within said chamber;

b. heating said wire mesh to promote adherence of the later depositedmaterial;

0. directing an electron beam onto said source of material to evaporatesaid material and deposit said material upon the heated wire surfaceexposed to the source of material so that the wire dimension in thedirection normal to the surface exposed to said material source isincreased.

11. Method of producing a generally planar fine conductive mesh whichhas a generally rectangular crosssection, with the cross-sectiondimension in the direction normal to the plane of the mesh beingsubstantially greater than the other cross-section dimension, whichmethod comprises;

a. disposing a uniform cross-section conductive mesh within an evacuatedchamber which is maintained at less than about 8 10 Torr pressure, withthe mesh disposed in a plane generally normal to the posed to theevaporated compatible conductive metal, so that the mesh cross-sectiondimension in the direction normal to the exposed surface and the planeof the mesh is increased, while the mesh cross-section dimension in theother direction is substantially unchanged.

1. METHOD OF PRODUCING FINE WIRE HAVING AN ELONGATED GENERALLYRECTANGULAR CROSS-SECTION, WHICH WIRE HAS A CROSS-SECTION WHICH IN AFIRST DIRECTION IS OF A PREDETERMINED DIMENSION, AND IN A SECONDDIRECTION NORMAL TO THE FIRST DIRECTION HAS A SIGNIFICANTLY GREATERDIMENSION, WHICH METHOD COMPRISES: A. DISPOSING A WIRE WITHIN ANEVACUATED CHAMBER WHICH IS MAINTAINED AT LESS THAN ABOUT 8X10**-6 TORRPRESSURE, WITH THE WIRE DISPOSED ABOVE AN EVAPORABLE SOURCE OF MATERIALDISPOSED WITHIN SAID CHAMBER, B. HEATING SAID WIRE TO PROMOTE ADHERENCEOF THE LATER DEPOSITED MATERIAL, C. DIRECTING AN ELECTRON BEAM ONTO SAIDSOURCE OF MATERIAL TO EVAPORATE SAID MATERIAL AND DEPOSIT SAID MATERIALUPON THE HEATED WIRE SURFACE EXPOSED TO THE SOURCE OF MATERIAL SO THATTHE DIMENSION IN THE DIRECTION NORMAL TO THE SURFACE EXPOSED TO SAIDMATERIAL SOURCE IS INCREASED.
 2. The method specified in claim 1,wherein said wire comprises a generally planar fine wire mesh.
 3. Themethod specified in claim 1, wherein the wire is preferably nickel offrom 0.1 to 1 mil thick, and a first tantalum layer is electron beamevaporated and deposited thereon, after which nickel is electron beamevaporated and deposited on the tantalum.
 4. The method specifieD inclaim 3, wherein the fine wire is initially approximately from 0.1 to 1mil in thickness and the deposition increase is substantially only inthe wire thickness.
 5. The method specified in claim 1 whereinsuccessive layers of different material are sequentially evaporated byelectron beam heating and deposited upon the heated wire surface.
 6. Themethod specified in claim 5, wherein for a nickel wire startingmaterial, tantalum is first evaporated and deposited upon the nickelwire, and thereafter nickel is evaporated and deposited atop thetantalum.
 7. The method specified in claim 1 wherein the electron beampower is up to about 10,000 watts.
 8. The method specified in claim 1,wherein the wire is heated at a power input of about 500-1500 watts forabout 45 minutes prior to the electron beam evaporation depositionprocess.
 9. The method specified in claim 1 wherein the wire comprises afine mesh, with the wire thickness being between 0.1 to 1 mil, and themesh has up to about 2000 wires per inch.
 10. Fine wire of selectedconductive material having an elongated generally rectangularcross-section produced by the method of: a. disposing a uniformcross-section wire mesh within an evacuated chamber which is maintainedat less than about 8 X 10 6 Torr pressure, with the wire mesh beingdisposed above an evaporable source of material disposed within saidchamber; b. heating said wire mesh to promote adherence of the laterdeposited material; c. directing an electron beam onto said source ofmaterial to evaporate said material and deposit said material upon theheated wire surface exposed to the source of material so that the wiredimension in the direction normal to the surface exposed to saidmaterial source is increased.
 11. Method of producing a generally planarfine conductive mesh which has a generally rectangular cross-section,with the cross-section dimension in the direction normal to the plane ofthe mesh being substantially greater than the other cross-sectiondimension, which method comprises; a. disposing a uniform cross-sectionconductive mesh within an evacuated chamber which is maintained at lessthan about 8 X 10 6 Torr pressure, with the mesh disposed in a planegenerally normal to the path between the mesh and an evaporablecompatible conductive metal; b. heating the mesh to promote adherence ofthe later deposited compatible conductive metal; c. directing anelectron beam onto the compatible conductive metal to evaporate same,and thereby deposit same, upon the heated mesh surface exposed to theevaporated compatible conductive metal, so that the mesh cross-sectiondimension in the direction normal to the exposed surface and the planeof the mesh is increased, while the mesh cross-section dimension in theother direction is substantially unchanged.